The present invention relates generally to elevators and more specifically to a device for determining the position of an elevator car.
Absolute position reference systems are known in the prior art. U.S. Pat. No. 5,023,434 relates to a position indicating apparatus particularly for overhead transport systems. The position indicating apparatus includes an elongated code carrier carrying multi-value code marks along its length. A code reading device secured on a transport carrier, such as a trolley, crane, or other traveling mechanism, reads the code marks on the code carrier. To prevent erroneous reading when the transport carrier and thus the code reading device is tilted or skewed with respect to the code carrier, and to ensure accuracy of position of reading of the code carrier, the code marks are arranged on the code carrier, one next to another in a single row or track, and formed such that “m” of the code marks provides one code word, the code words being positioned one next to each other and appear only once, or are unique along the entire code carrier. The code reader has a reading station, for each bit, with three sets of reading heads per station which are equidistantly distributed by a distance corresponding at least to the number of digits of a code word to provide, upon processing of outputs from all three reading heads, an unambiguous position indication.
U.S. Pat. No. 5,138,560 to Lanfer et al. illustrates a position indicating apparatus which includes a code carrier which carries multi-value code marks in one track along its length. The code marks are combined into blocks with which a block identification is associated. Cooperating with the code carrier and the block identification are a code reader and an auxiliary reader, respectively. Along the travel path, the code carrier and the code reader are disposed counter to one another. To enable increasing the length of the addressable travel paths without losing positional accuracy, or without having to increase the number of code marks in one code word, a block identification is associated with the blocks. From the block identification, an auxiliary reader can recognize whether the code reader is reading only code marks from one block. In this way, the travel path can be divided into important zones, in which the accurate position of the vehicle must be known, and to which blocks must therefore be assigned, and unimportant zones, which are merely gaps between blocks that connect the important zones to one another.
U.S. Pat. No. 5,821,477 to Gerstenkorn illustrates a reflector mounted in an elevator shaft and having coded symbols in two tracks in the region of a stopping floor. Detectors on a car read the coded symbols for bridging door contacts when the car is in the arrival region and the resetting region of the stopping floor. The symbols are detected and evaluated by a two-channel evaluating circuit having optical transmitters for illuminating the tracks and charge-coupled device sensors for detecting the reflected images. A pattern recognition logic system and computers for each channel recognize patterns in the images for generating car position and speed information and for actuating relays to bridge the door contacts.
U.S. Pat. No. 6,435,315 to Zaharia relates to an apparatus for determining the position of an elevator car within a hoistway that includes a code rail containing optically readable indicia that is being mounted within the hoistway adjacent to the path of travel of the car. At least one camera is mounted upon the car for movement therewith for scanning the code rail indicia and providing data indicative of the car's position to the car controllers.
PCT Publication WO 01/83352 to Wegener et al. relates to a device for determining the position of an elevator car during evacuation which includes an endless cable that is connected to the elevator car and provided with marks. A unit for detecting the marks is provided.
While these position referencing systems work well, there is still a need for better systems without additional equipment along the travel path, e.g., elevator hoistway walls.